Preparations for Birth

Getting fat is the most important preparation for birth. After
mating in late May or June, pregnant females focus on eating for the
rest of the summer. Females that don't become fat enough by fall
cannot maintain their pregnancies.

Around Ely, females that
weigh 176 or more by fall maintain pregnancies, give birth in dens in
mid to late January, and provide enough milk for their cubs to
survive. Females that weigh less than 148 pounds in fall do not give
birth. Females of intermediate weights may or may not give birth, and
cubs from those females are less likely to survive.

The Cubs Develop

By the end of February, cubs are 4 to 6 weeks old and usually weigh 2-3 pounds. They have dense fur almost an inch long. They can thermo-regulate to some extent, but they still cry for help staying warm and fed. They can crawl, but they can't walk. Their eyes are opening or fully open.

On warmer days, with temperatures in the 20's, the cubs often sleep partially exposed on their mother's back.

Care of Newborn Cubs

Newborn cubs are smaller, relative to their mother's size, than the
young of any other placental mammal. They are totally dependent on
their mothers. Newborn cubs have little fur, weigh less than a pound,
and can barely crawl. Three cubs is the most common litter size around
Ely.

Around Ely, temperatures at the time of birth in January
can be 60 degrees (F) below zero. Most dens are no warmer than the
outside air because most den entrances are open. Some "dens" are
simply nests on the ground surface.

Dealing with Water in the Den

Water in dens is a problem, especially for mothers with cubs. Newborn cubs that are too young to walk in January, February, or early March can be killed from exposure or drowning if there is an early melt or hard rain.

By mid-March, cubs have enough fur and mobility to deal with wetness with help from their mothers. Some cubs take refuge on their mothers' backs. Sometimes, the whole family can find a drier spot in the den. Melt water that drips on cubs is licked off by the mothers.